Stray Light Calibration of the EnMAP Imaging Spectrometer Mission

Abstract

The German imaging spectrometer mission EnMAP, consisting of a Visible and Near-InfraRed (VNIR) (418.2 nm to 993.0 nm) and a Short Wavelength InfraRed (SWIR) (902.2 nm to 2445.5 nm) spectrometer, was successfully launched on 1 April 2022. In this work, we report EnMAP's on-ground stray light calibration measurements and their results. Using a custom-built light source and a collimator, we determined the diffuse stray light by measuring the point spread functions at twelve spatial and fifteen (11 VNIR, 4 SWIR) spectral positions with a dynamic range of up to 10^9. Additionally, we measured the out of field stray light in along-track direction over an angular range of \pm0.2°. For both types of stray light, we present a correction method and use simulations to demonstrate the effect on a test scene. Finally, we show lunar contrast measurements that were used to check EnMAP's in-orbit performance. The results indicate that stray light has a negligible impact on EnMAP's radiometric uncertainty.